Drug delivery devices, which are handled by patients themselves and allow individual dosing of the required amount of drug are well known in the art. Generally, such devices have substantially the same purpose as that of an ordinary syringe. A device of the mechanical pen-type is known, e.g., from U.S. Pat. No. 5,226,895.
In such devices, usually a needle assembly comprising a double-ended needle is attached to the device at its distal end. A drug containing cartridge is mounted in a distal end portion of the housing between the needle and a piston rod driving the piston in the cartridge for dispensing the liquid, which is moved by a drive mechanism.
A removable needle cover is mounted on the distal end of the needle to protect the needle from contamination and damage. Further, a removable cap is mounted at the distal end of the housing of the device. The cap is designed to cover and protect the needle and needle cover.
Prior to injection the user (patient, caregiver etc.), must remove the cap from the distal end of the housing and the needle cover from the distal end of the needle. After injection, the needle cover is put back onto the needle and the cap onto the distal end of the housing.